1. Field of the Invention
The present invention relates generally to the field of semiconductor fabrication and, more particularly, to a two-step method for reliably etching a very-high aspect ratio fuse window on a semiconductor substrate involving the use of advanced process control (APC). The remaining thickness of the target layer at the bottom of the fuse window can be precisely controlled.
2. Description of the Prior Art
Semiconductor devices having a redundancy circuit for disabling defects components are known in the art. Most redundancy circuits have fuse interconnect-wires. The fuse interconnect-wires may be blown when applied with a laser beam, to disconnect the defective components from the normally functioning components.
FIG. 1 illustrates a typical cross-section view of a fuse interconnect-wire 10 that is formed concurrently with a multi-layered interconnect-wire structure 12 on a silicon substrate 100. As shown in FIG. 1, the interconnect-wire structure 12 comprises a lower inlaid wire layer 122 that is generally formed of copper by using copper damascene processes. The lower inlaid wire layer 122 may be, but not limited to, a fifth metal (M5) layer of the multi-layered interconnect-wire structure 12 wherein the first to fourth metal (M1-M4) layers are not shown in this figure for the sake of simplicity. The lower inlaid wire (M5) layer 122 is embedded in an insulating dielectric layer 113 and etch stop layer 114.
The interconnect-wire structure 12 further comprises an inlaid wire (M6) layer 124 embedded in an insulating dielectric layer 109 and etch stop layer 110. The inlaid wire (M6) layer 124 is electrically interconnected with the lower inlaid wire (M5) layer 122 through the via 123 that is embedded in the insulating dielectric layer 111 and cap layer 112. The interconnect-wire structure 12 further comprises an inlaid wire (M7) layer 126 embedded in an insulating dielectric layer 105 and etch stop layer 106. The inlaid wire (M7) layer 126 is electrically interconnected with the inlaid wire (M6) layer 124 through via 125 that is embedded in the insulating dielectric layer 107 and cap layer 108. The interconnect-wire structure 12 further comprises a bonding pad layer 128 that is generally formed of Al, AlCu, Cu, or a composite.
The bonding pad layer 128 is electrically interconnected with the underlying inlaid wire (M7) layer 126 through via 127 that is embedded in the insulating dielectric layer 103 and cap layer 104. The bonding pad layer 128 is protected with a passivation layer 101 and dielectric layer 102. An opening 130 is formed in the passivation layer 101 to expose a portion of the top surface of the bonding pad layer 128.
Typically, the insulating dielectric layers 105, 107, 109, 111 and 113 are made of low dielectric constant (low-k) materials such as FSG or the like. The etch stop layers 106, 110 and 114 are made of PECVD nitride, LPCVD nitride or oxy-nitride. The cap layers 104, 108, 110 and 112 are made of PECVD nitride, LPCVD nitride, carbide, silicon carbonitride or oxy-nitride. The dielectric layer 102 is generally formed of silicon oxide such as PECVD oxide. The passivation layer 101 is generally formed of silicon nitride.
In this case, the fuse interconnect-wire 10 is formed concurrently with the lower inlaid wire (M5) layer 122 of the interconnect-wire structure 12. A so-called fuse window for laser ablation is provided directly above the fuse interconnect-wire 10. The fuse window is a recessed opening with a very-high aspect ratio that is located directed above the fuse interconnect-wire 10 with the bottom of the fuse window not exposing the fuse interconnect-wire 10.
The process for etching the fuse window is illustrated through FIGS. 2-4. As shown in FIG. 2, a photoresist layer 150 is coated on the passivation layer 101. A typical lithographic process is carried out to form an opening 160 in the photoresist layer 150. The opening 160 is situated directly above the fuse interconnect-wire 10 and defines the fuse window to be etched into the substrate 100. As shown in FIG. 3, a single-step non-stop dry etching process is then carried to consecutively etch the layers 101-111, thereby forming a fuse window 200 having a depth of, for example, 40000-50000 angstroms. In this case, a total of 11 consecutive layers including five different types of dielectric materials are etched.
Since the fuse interconnect-wire 10 is subject to oxidation, it is undesired to fully open the bottom of the fuse window 200 to thereby expose the surface of the fuse interconnect-wire 10. It is required that the single-step non-stop dry etching process eventually stops on the insulating dielectric layer 111, hereinafter also referred to as “target layer”. In order to increase the reliability of the fuse blow, it is important to control the remaining thickness of the target layer 111. Normally, it is desired to form a fuse window 200 with a target layer 111 having a remaining thickness of about 2000 angstroms. As shown in FIG. 4, after measuring the remaining thickness of the etched target layer 111, the photoresist layer 150 is then stripped.
However, the prior art single-step non-stop dry etching process is time-consuming and is not reliable. According to the prior art, the single-step non-stop dry etching process is carried out using endpoint mode and has to employ different etching recipes for selectively etching corresponding consecutive material layers above the target layer 111 under said endpoint mode. According to the prior art, the respective etching rates for etching through the consecutive layers 101-111 are basically different. The complex dielectric film stack (typically eleven consecutive layers with five different dielectric materials) over the fuse interconnect-wire 10 introduces variations and accumulated errors of the final result, and the out of spec (OOS) ratio is usually as high as 50% or even higher. Also, the low transition rate during the etching of the fuse window is another problem and most of final products have to be processed and tuned again after measurement, therefore, more manufacturing trouble is incurred. In light of the above, there is a need in this industry to provide an improved method for forming the fuse window.